‘Byzantium also required eunuchs to serve in the imperial palace, where they were taken on a variety of important functions. Some military commanders were eunuchs, while in the Eastern Church eunuchs could rise to the position of patriarchs. […] However, not all eunuchs were successful. Those who never joined the wealthy houses could still be found on the outskirts of the cities, serving as entertainment and even prostitutes in lower neighborhoods. ‘ [4]

That Christian society, and especially the Church itself – Roman or Orthodox – has an embarrassing relationship with eunuchs is a clear fact. Even more considering that the Papacy made official use of eunuchs in Sistine corals until the beginning of the 20th century [5], a practice abandoned due to extensive public criticism at the time and the fact that castration for corals was banned in Italy since 1861.

Islam, like Judaism and Christianity, had a solemn and inviolable ban on castration at its formation's basis. It is recalled in the Islamic tradition that the Prophet Muhammad would have said about the castrators of slaves: "whoever castrates them, we will castrate him" (Sunan na-Nasai. Hadith 4736)

Unlike the Christian Church, which allowed itself to be accommodated and even happily incorporated the pagan custom of castration for the most diverse and superfluous purposes, Islam remained stricter at its own prohibitions.

Not that this, of course, prevented Islamic societies from seeing eunuch servants at the highest esteem: they did not establish dynasties or practice nepotism, and were the most suitable guardians of harems. But as Sharia prohibited the castration process, punishing offenders under the Lex Talionis principle (the Muslim who castrates will be punished with castration), there were legal ways of acquiring them without breaking the Prophet’s law: commerce and razias. As the chronicler and eyewitness al-Muqaddasi, in the 10th century, describes:

‘When I asked a group of them about the castration process, I was informed that the Romans [Byzantines] castrate their young people with the intention of dedicating them to the Church […] When Muslims carry out robberies, they attack churches and take their youth’ [7]

As noted by Mary Valante in her book “Monks Castrators”:

‘Arab raids were deliberately targeting Greek churches and monasteries […] at a time when the Greeks castrated certain young boys to keep them as singers in the Church and at a time when the Arab World wanted eunuchs.’ [8]

In addition to the pillaging campaigns in churches, another opportunity to acquire eunuchs came from commerce with the Northmen.

https://historiaislamica.com/en/eunuchs-castrated-by-the-churches-and-sold-to-the-arabs/

The practice of castration was not limited to the Latin and Greek churches. At the same time that Rome was abandoning Castratos for public consternation that fueled European anticlericalism, Coptic Christians were active castrators. American scholars record the activity of Coptic priests emasculating slave boys in Egypt in 1898 [11], 1900 [12] and 1919 [13], as well as in even later decades.

The boys were stuck on boards, so as not to resist the surgery, which consisted of removing the penis and testicles with a sharp razor. The real problem, however, came from post-surgery’s infections. To prevent this, immediately after the cut, the priest-surgeon would insert a piece of bamboo into the urethra, thus allowing a channel of urine ejection. The new eunuch was then buried in a sand pit up to the height of his neck, being left under strong sunlight for two or three days until there was no more risk of infection [14].

“Each eunuch castrated in a simple way costs around 200 dollars. The country’s largest eunuch factory, however, is found on Mount Ghebel-Eter, in Abou-Gerghè. Here, at a large Coptic monastery, where the unfortunate African children are gathered. […] Coptic monks operate in a lucrative business, supplying Constantinople, Arabia and Asia Minor with their highly sought after – and expensive – eunuchs. Two types come from here: those simply castrated and those with complete organ ablation; the second type [of eunuch] is sold at about 750 or 1,000 dollars a head. “[14]

(http://www.autoadmit.com/thread.php?thread_id=5532156&forum_id=2#47688382)